interface A6_1{
  double f(double x,double y);
}
class B6_1 implements A6_1{
  public double f(double x,double y){
    return x*y;
  }
  int g(int a,int b){
    return a+b;
  }
}
public class E6_1 {
  public static void main (String args[]){
    A6_1 a=new B6_1();
    System.out.println(a.f(3,5));
    B6_1 b=(B6_1)a;
    System.out.println(b.g(3,5));
  }
}
